1. Field of the Invention
This invention relates to an orthopedic trial femoral component for use in determining the correct prosthetic femoral component for implantation from a group of prosthetic femoral components. More particularly, this invention relates to a two-piece trial component to be used as a guide for the surgeon in selecting the proper sized prosthetic femoral component.
2. Description of the Prior Art
Orthopedic surgery to replace a femur head and neck with a prosthetic component or to replace a previously implanted femoral prosthetic device is a complex operation requiring a relatively lengthy surgery. There has been a need to shorten and simplify this procedure while simultaneously providing the best fit between the prepared femoral canal and the prosthetic implant. This is especially true since many of the patients requiring such surgery are elderly or multi-trauma patients who require a series of operations and the longer the patient is under anesthesia, the greater the risk.
To determine the appropriate femoral implant size, the surgeon takes and examines X-rays of the femur. He then uses a trial component as a guide in preparing the femur to receive the chosen prosthesis. The surgeon attempts to select a trial implant which fits so that his final implant will likewise fit.
In the past, surgeons have used a series of one-piece trial prostheses which were identical in size to corresponding prosthetic implants. These prosthetic femoral implants came in discrete sizes which had been determined to cover the widest range of patients that surgeons were likely to encounter.
The surgeon would prepare the femoral canal by rasping and/or reaming and through guesswork, he would determine if the one-piece femoral trial prosthesis fit. Difficulties were encountered with a one-piece femoral trial-prosthesis because the proximal body of the trial prosthesis blocked the view of the medullary canal and this made it difficult to determine the correct one-piece prosthesis. The surgeon, upon implementation, often found that either his preparation of the femur was incorrect or the geometry of the prepared femur did not allow for the preliminarily chosen femoral implant to be used. Often it was extremely difficult to discern whether the problem or obstruction was located distally around the stem or proximally around the body portion of the trial prosthesis.
Manufacturers compensated for these difficulties by providing a series of femoral prosthetic implants with identical stem lengths but different neck/body sizes or vice versa. The surgeon also was provided with a series of one-piece trial prostheses with multiple stem and body sizes. The surgeon then used trial and error methods to determine the best fitting trial prosthesis from the different trial prostheses.
To overcome this position, modular two-piece trial prostheses were developed such as disclosed in U.S. Pat. No. 5,100,407. The disclosed modular trial system provides a two-piece trial component kit with a plurality of interchangeable heads and stems. This two-piece trial prosthesis separates the head and neck region of the trial prosthesis from the stem portion to provide the surgeon with a cross-sectional view of the bone where the surgeon cuts the femur. With this two-piece trial system, the stem and proximal body components of the femoral trial prosthesis are fitted separately so that the surgeon can address each fit independently and more easily.
The two-piece trial prosthesis of U.S. Pat. No. 5,100,407 is particularly adapted for resection cases where the surgeon must remove the head and neck of the femur in order to replace it with a femoral implant. The surgeon prepares a bone bed for the proximal body component of the two-piece trial prosthesis by using the trial proximal component as a guide for the necessary proximal cut of the femur and/or to check the accuracy of his rough cut.
The surgeon then moves onto fitting the distal trial stem component by first inserting various trial stem sizes to see which fits the patient best. The surgeon can quickly access the stem fit because there is no proximal head and body to block his view so he can clearly see the stem within the femoral canal. In the one-piece system, it would not be possible to view the distal fit because the integral head/body would obstruct the surgeon's view.
In the described two-piece trial system, the trial prosthesis is composed of a stem component and a body component, thus the distal and proximal fit of the stem within the femoral canal is addressed by use of a single trial component. Therefore, it is not always possible to size the stem of the prosthesis both distally and proximally within the femoral canal. In revision cases, where a previous femoral implant is being replaced and the epiphysis of the femur is gone, it becomes increasingly important to fit the femoral canal with the implant along its entire length. Thus, there has been a need in the art for a trial prosthesis which adequately address the aforementioned difficulties and drawbacks of existing devices.